Patent GB-1416026-A (GB)
Title: Hydrostatic transmission speed control system
IPC: F16H61/4008
Filed: 1972-10-30
Abstract: 1416026 Hydrostatic transmissions; full-face disc brakes MASSEY-FERGUSON SERVICES NV 30 Oct 1972 [1 Nov 1971] 49919/72 Headings F2W and F2E In a hydrostatic transmission comprising a variable displacement pump 10 and a motor 8 of fixed (as shown) or variable displacement, the output shaft 24 of the transmission is provided with an hydraulically operated brake 88 which can only be actuated when the transmission is in neutral and variable relief valves 186 and 186a are provided between the working circuit conduits 16 and 18 which open at a lower pressure when the brake 88 is in operation than when it is not. The output shaft 24 is connected to the planet carrier 28 of epicyclic gearing 3, the sun gear 30 of which is driven by the input shaft 4 of the transmission and the ring gear 26 of which is driven by the motor 8, so that the motor 8 has to be driven by the pump 10 in the neutral condition of the transmission to counteract the rotation of sun gear 30 and hold shaft 24 stationary. Braking.-Operation of brake 88 is effected by two valves, a valve 100, Fig. 1a, which receives fluid from a pressure source to its port 96 and supplies this to a port 104 in the brake activated position shown of a spool 112, or to a sump via port 102, and a valve 110, Fig. 2, which controls communication between the port 104 of valve 100 and the brake 88, the valve 110 having an inlet port 120 connected to port 104 by a line 106 and an outlet port 122 connected to brake 88 by a line 94. The valve 110 has a valve plunger 126 urged by a spring 128 towards a lever 136. The lever 136 has a recess 142 engageable by a roller 146 on a member 144 which pivots with the swash plate 12 of pump 10, the recess 142 being engaged by roller 146 in the neutral condition of the transmission. Engagement of recess 142 and roller 146 allows movement of lever 136 to move the plunger 126 to allow fluid to be supplied to the brake 88. The brake 88 can thus only be actuated in neutral. For braking, axially-slidable non-rotary disc 92 is urged into contact with disc 90, rotatable with shaft 24. Variable relief valves.-The working circuit 16, 18 is connected by lines 162, 164 to chambers 158, 160 of a valve body 150 incorporating variable relief valves 186, 186a Each valve 186, 186a comprises a spring 204 loaded piston 198 having an orifice 202 to allow equal pressures on both its sides to close communication between chambers 158, 160, the chamber on one side of piston 198 having an orifice 206 normally closed by a valve member 208 under the bias of a spring 210, the opposite end of which bears against a wall of a piston 212. On pressure in the main line, e.g. 18, increasing above its limiting valve the pressure in chamber 158 will cause piston 208 to move against its spring 210 and thereby reduce pressure on one side of piston 198, to move this piston and so interconnect chambers 158 and 160, and hence lines 16 and 18. When brake valve 100 is actuated each relief valve 186, 186a receives pressure at a port 218, 218a, which moves piston 212 and so reduces the force of spring 210 on valve member 208 and reduces the maximum pressure permitted in the working circuit. The valve body 150 also includes check valves 184, 184a for supply of make up fluid from a feed pump 170. Pump control.-The pump displacement is adjusted by a cylinder 46 having a piston 47, the rod 48 of which is attached to the swash plate 12 and pressure to which is controlled by a control valve 36 having a spool movable by pivoting of a lever assembly to supply pressure from a source, received through line 40, to either side of the piston 47. The linkage for moving the spool of valve 36 is attached to the swash plate 12 by link 54 to provide a mechanical follow-up action. The lever assembly 58 comprises a first lever 61, attached to the control lever 228 (Fig. 5) by a link 246, and a further lever 59 attached through a spring 63 to lever 61, the lever 59 being connected by further linkwork to valve 36. A pedal 62, when depressed, rotates a plate 78 provided with pins 80, 82 which engage a lever 84 to thereby return the transmission to neutral for inclining and, due to the spring connection between levers 59 and 61, the lever 59 may move whilst the lever 61 remains in its set position so that, on release of pedal 62, the transmission returns to its original condition through the action of spring 63. The control lever 218 is moved back and forth through a slot 226 for variation of transmission ratio and, at the position (228b) corresponding to neutral, can be moved transversely to adjust the valve 100 for braking (via a lever 250, Fig. 4 not shown).